Relaxation of phasic contractile activity of human detrusor strips by cyclic nucleotide phosphodiesterase type 4 inhibition

Expression of Phosphodiesterase (PDE) Isoenzymes in the Human Male and Female Urethra

Purpose

Although it has been supposed that the NO/cyclic GMP system produces inhibitory signals to reduce the resistance of the bladder outlet and urethra during the micturition phase, little is known on the mechanisms controlling the function of urethral smooth muscle. The aim of the present study was to examine in the male and female urethra the expression of phosphodiesterase (PDE) isoenzymes, known as key proteins of the cyclic GMP/AMP signaling.

Methods

Urethral tissue was obtained from 4 female cadavers and 7 male patients (who had undergone gender reassignment surgery). The expression of mRNA encoding for PDE1A, 1B, 1C, 2A, 4B, 4D, 5A, 10A and 11A was investigated by means of real-time polymerase chain reaction. Western blot (WB) analysis was conducted to detect PDE isoenzymes.

Results

RT-PCR revealed relevant amounts of mRNA encoding for PDE1A, 2A, 4B, 5A, 10A and 11A in male and female urethral tissue. The expression of PDE1A, 2A, 4B and 10A was 2-fold higher in the female than in the male urethra, whereas the expression of PDE11A mRNA was 7-fold higher in the male tissue. In the WB experiments, immunosignals specific for PDE1A, PDE4A and 4B and PDE11A were of higher degree in the female than the male tissue specimens, while an almost equivocal expression of PDE2A, PDE5A and PDE10A was registered.

Conclusion

On the level of mRNA and function proteins, different patterns of expression of PDE isoenzymes were registered in human male and female urethra. Future studies may clarify whether inhibition of PDE isoenzymes is likely to facilitate the relaxation of the outflow region in both sexes.

Combination phosphodiesterase type 4 inhibitor and phosphodiesterase type 5 inhibitor treatment reduces non-voiding contraction in a rat model of overactive bladder

Introduction

Current treatments for overactive bladder (OAB) are often discontinued due to side effects or lack of efficacy. The goal of this study was to determine if combining a phosphodiesterase type 4 inhibitor (PDE4i); with a type 5 inhibitor (PDE5i); would have a beneficial effect on OAB symptoms and if a reduced dose of PDE4i in combination with PDE5i could also provide a beneficial effect in OAB. We hypothesized that PDE5i and PDE4i combination treatment could be utilized to reduce non-voiding contractions and smooth muscle disruption in a rat model of OAB.

Methods

Fifty-eight age-matched Sprague-Dawley rats underwent PBOO and daily gavage with PDE4i alone (roflumilast; 1mg/kg), PDE5i alone (tadalafil;10mg/kg), high dose combination (PDE4i 1mg/kg, PDE5i 10mg/kg), low dose combination (PDE4i 0.2mg/kg, PDE5i 10mg/kg), or vehicle for 28 days. Fourteen animals underwent sham PBOO with vehicle. Rats underwent conscious and anesthetized cystometry 28 days after PBOO and were euthanized for qualitative bladder histology. One-way ANOVA on ranks with a Dunn’s post hoc test was used to indicate statistically significant differences between groups (p<0.05).

Results

Bladder & urethral weight was significantly increased after PBOO with vehicle, PDE4i alone, and PDE5i alone, but not with either combination treatment. Frequency of non-voiding contractions during both conscious and anesthetized cystometry increased significantly after PBOO with vehicle, but not after PDE4i or high dose combination treatments compared to sham PBOO. Threshold pressure for voiding was significantly decreased with high dose combination compared to vehicle. PBOO treated with PDE4i alone or high dose combination showed less bladder smooth muscle fibrosis than vehicle, PDE5i alone, or low dose combination treatments.

Conclusion

A PDE4i and PDE5i combination treatment has potential benefit in reducing OAB symptoms, but future research is needed.

The phosphodiesterase type 4 inhibitor roflumilast suppresses inflammation to improve diabetic bladder dysfunction rats

PURPOSE

To demonstrate that phosphodiesterase type 4 (PDE4) inhibitors could potentially treat diabetic bladder dysfunction (DBD) through modulation of the systemic inflammatory response.

METHODS

In this 6-week study, 60 female Sprague-Dawley rats were divided into three groups: (i) vehicle-treated control rats; (ii) vehicle-treated streptozocin (STZ)-injected rats; and (iii) roflumilast-treated STZ-injected rats. Oral roflumilast (5 mg/kg/day) was administered during the last 4 weeks of STZ injection to induce diabetes in the test group. At 6 weeks, a urodynamic study was performed in each group. The expression of nuclear factor kappa B (NF-κB), tumor necrosis factor-alpha (TNF-α), interleukin (IL)-6, and IL-1β in detrusor smooth muscle (DSM) was analyzed using quantitative reverse transcription-polymerase chain reaction and Western blotting.

RESULTS

A significant decrease in bodyweight and significant increases in bladder weight and blood glucose level were observed in the diabetic rats and were not ameliorated by roflumilast treatment. Cystometry showed the increased bladder capacity, voiding volume, residual urine volume, and voiding interval in the diabetic rats and the prevention of these changes by roflumilast. These changes were accompanied by significantly enhanced expression of NF-κB, TNF-α, IL-6, and IL-1β in DSM tissue from diabetic rats. Furthermore, roflumilast attenuated the expression of inflammatory factors in DSM tissue.

CONCLUSIONS

Oral treatment with roflumilast in diabetic rats improves bladder function and inhibits the expression of inflammatory factors in DSM tissue, indicating that PDE4 is a potential therapeutic target for DBD.

Beneficial effects of rolipram, a phosphodiesterase 4 specific inhibitor, on testicular torsion-detorsion injury in rats

INTRODUCTION

The aim of the study is to investigate the effect of Rolipram, a selective phosphodiesterase 4 inhibitor, on testicular torsion - detorsion injury.

METHODS

Sixty young male rats were divided into five groups. In each group, the right testes of six rats were removed four hours after detorsion for biochemical analysis, and the right testes of the remaining six rats were removed 24 h after detorsion for pathological analysis. In group 1 (sham-operated) right orchiectomy was performed without torsion, and right testes were sent to the laboratory for biochemical and pathologic analyses. In group 2 (control) torsion was applied to the right testes for 60 min, and detorsion was performed without the administration of Rolipram. In group 3 torsion was applied to the right testes for 60 min. 1 mg/kg Rolipram was administered 30 min before detorsion. In group 4 torsion was applied to the right testes for 60 min, and 1 mg/kg Rolipram was administered during detorsion. In group 5 torsion was applied to the right testes for 60 min. 1 mg/kg Rolipram was administered 30 min after detorsion. The malondialdehyde and nitric oxide levels were determined. The rates of necrosis and apoptosis were evaluated by histopathological examination.

RESULTS

The level of malondialdehyde was higher in the torsioned groups (Group 2, 3, 4, 5) than that in group 1 (p = 0.004). There was no statistically significant difference between the groups regarding the level of nitric oxide (p = 0.182). Apoptosis was higher in groups 2, 3 and 4 than in group 1; however, apoptosis was similar in group 1 and group 5 (p = 0.122). The level of necrosis in group 1 was similar to that in groups 4 and 5 (p = 0.194 and p = 0.847, respectively).

CONCLUSION

We suggest that the administration of Rolipram can decrease the rate of necrosis and apoptosis in testicular ischaemia-reperfusion injury.

Inhibition of Multidrug Resistance Proteins by MK 571 Enhances Bladder, Prostate, and Urethra Relaxation through cAMP or cGMP Accumulation

The biologic effect of cAMP and cGMP is terminated by phosphodiesterases and multidrug resistance proteins MRP4 and MRP5, which pump cyclic nucleotides out of the cell. Therefore, this study aimed to characterize the role of MRP inhibitor, MK 571 (3-[[[3-[(1E)-2-(7-chloro-2-quinolinyl)ethenyl]phenyl][[3-(dimethylamino)-3-oxopropyl]thio]methyl]thio]propanoic acid), in the bladder, prostate, and urethra of male mice by means of functional assays, protein expression, and cyclic nucleotide quantification. The cumulative addition of MK 571 (1-30 µM) produced only small relaxation responses (approximately 25%) in all studied tissues. In the bladder, isoprenaline/fenoterol and forskolin concentration-dependently relaxed and MK 571 (20 µM) increased the maximal response values by 37% and 24%, respectively. When MK 571 was coincubated with fenoterol or forskolin, intracellular levels of cAMP and protein expression of phospho-vasodilator-stimulated phosphoprotein (p-VASP) Ser157 were significantly greater compared with bladders stimulated with fenoterol or forskolin alone. In the prostate and urethra, sodium nitroprusside concentration-dependently relaxed and MK 571 (20 µM) significantly increased relaxation responses by 70% and 56%, respectively, accompanied by greater intracellular levels of cGMP and protein expression of p-VASP Ser239 in the prostate. Tadalafil and BAY 41-2272 (5-cyclopropyl-2-[1-[(2-fluorophenyl)methyl]-1H-pyrazolo[3,4-b]pyridin-3-yl]-4-pyrimidinamine) also relaxed the prostate and urethra, respectively, and MK 571 markedly enhanced this response. The stable analog of cGMP (8-Br-cGMP) induced concentration-dependent relaxation responses in the prostate and urethra, and MK 571 significantly increased the relaxation response. In conclusion, to our knowledge, this is the first study to show that efflux transporters are physiologically active in the bladder, prostate, and urethra to control intracellular levels of cAMP or cGMP.

Phosphodiesterase type 4 inhibition enhances nitric oxide- and hydrogen sulfide-mediated bladder neck inhibitory neurotransmission

Nitric oxide (NO) and hydrogen sulfide (H₂S) play a pivotal role in nerve-mediated relaxation of the bladder outflow region. In the bladder neck, a marked phosphodiesterase type 4 (PDE4) expression has also been described and PDE4 inhibitors, as rolipram, produce smooth muscle relaxation. This study investigates the role of PDE4 isoenzyme in bladder neck gaseous inhibitory neurotransmission. We used Western blot and double immunohistochemical staining for the detection of NPP4 (PDE4) and PDE4A and organ baths for isometric force recording to roflumilast and tadalafil, PDE4 and PDE5, respectively, inhibitors in pig and human samples. Endogenous H₂S production measurement and electrical field stimulation (EFS) were also performed. A rich PDE4 and PDE4A expression was observed mainly limited to nerve fibers of the smooth muscle layer of both species. Moreover, roflumilast produced a much more potent smooth muscle relaxation than that induced by tadalafil. In porcine samples, H₂S generation was diminished by H₂S and NO synthase inhibition and augmented by roflumilast. Relaxations elicited by EFS were potentiated by roflumilast. These results suggest that PDE4, mainly PDE4A, is mostly located within nerve fibers of the pig and human bladder neck, where roflumilast produces a powerful smooth muscle relaxation. In pig, the fact that roflumilast increases endogenous H₂S production and EFS-induced relaxations suggests a modulation of PDE4 on NO- and H₂S-mediated inhibitory neurotransmission.

Investigational Drug Therapies for Overactive Bladder Syndrome: The Potential Alternatives to Anticolinergics

Background

Overactive bladder is a high prevalent and quality of life affecting disease. The mainstay of the medical therapy is represented by antimuscarinic drugs, but their side effects markedly affect patient compliance and prompt studies on novel investigational drugs.

Methods

A systematic literature search of peer-reviewed papers and meeting abstracts published by December 2008 was performed. PubMed databank was searched for original English articles, by using the following search terms: “overactive bladder” or “detrusor overactivity” or “urinary incontinence” and “treatment”, alone and linked to any potential molecular target or novel drug cited in the literature.

Results

Effective alternative pharmacological treatments are currently scarce, but many new promising compounds are emerging which target key molecular pathways involved in micturition control. The most promising potential therapeutic targets include central nervous system GABAergic inhibitory pathway, dopaminergic and serotoninergic systems, b-adrenoceptors and cAMP metabolism, nonadrenergic-noncholinergic mechanisms such as purinergic and neuropeptidergic systems, vanilloid receptor, bladder sensory nervous terminals, nonneuronal bladder signalling systems including urothelium and interstitial cells, prostanoids, Rho-kinase and different subtypes of potassium and calcium channels.

Conclusions

Despite the enormous amount of new biologic insight, very few novel pharmacological therapies seems to have passed the proof-of-concept clinical stage. The ultimate clinical utility of new drugs will depend on the ability to exploit tissue-specific differences and disease-related changes in molecular expression/function and to improve storage phase dysfunctions without interfering with the emptying phase. Further preclinical investigations and controlled clinical trials are urgently needed in this challenging field.

Treatment of obesity-associated overactive bladder by the phosphodiesterase type-4 inhibitor roflumilast

PURPOSE

To prove that phosphodiesterase type-4 inhibitors could potentially treat obesity-associated overactive bladder through modulation of the systemic inflammatory response.

METHODS

In this 12-week study, 90 female Sprague-Dawley rats were divided into three groups: (1) vehicle-treated normal diet (ND)-fed rats; (2) vehicle-treated high-fat diet (HFD)-fed rats; and (3) roflumilast-treated HFD-fed rats. Oral roflumilast (5 mg/kg/day) was administered during the last 4 weeks of HFD feeding in the test group. At 12 weeks, a urodynamic study was performed in ten rats of each group. Bladder tissue was extracted, the bladder mucosa was separated under microscopy, and bladder detrusor smooth muscle (DSM) expression of TNF-α, interleukin (IL)-6, IL-1β, and nuclear factor kappa B (NF-κB) were analyzed using Western blotting and quantitative reverse transcription-polymerase chain reaction (qRT-PCR).

RESULTS

Bodyweights of the HFD-fed rats significantly increased and were not ameliorated by roflumilast treatment. Cystometry evidenced augmented frequency and non-void contractions in obese rats that were also prevented by roflumilast. These alterations were accompanied by a markedly increased expression of TNF-α, IL-6, IL-1β, and NF-κB in DSM of obese rats. Furthermore, roflumilast decreased expression of inflammatory factors in DSM.

CONCLUSIONS

Oral treatment with roflumilast in rats fed an HFD restores normal bladder function and downregulates expression of inflammatory factors in the bladder.

Actions of cAMP on calcium sensitization in human detrusor smooth muscle contraction

OBJECTIVES

To clarify the effect of cAMP on the Ca(2+) -sensitized smooth muscle contraction in human detrusor, as well as the role of novel exchange protein directly activated by cAMP (Epac) in cAMP-mediated relaxation.

MATERIALS AND METHODS

All experimental protocols to record isometric tension force were performed using α-toxin-permeabilized human detrusor smooth muscle strips. The mechanisms of cAMP-mediated suppression of Ca(2+) sensitization activated by 10 μm carbachol (CCh) and 100 μm GTP were studied using a selective rho kinase (ROK) inhibitor, Y-27632, and a selective protein kinase C (PKC) inhibitor, GF-109203X. The relaxation mechanisms were further probed using a selective protein kinase A (PKA) activator, 6-Bnz-cAMP and a selective Epac activator, 8-pCPT-2'-O-Me-cAMP.

RESULTS

We observed that CCh-induced Ca(2+) sensitization was inhibited by cAMP in a concentration-dependent manner. GF-109203X (10 μm) but not Y-27632 (10 μm) significantly enhanced the relaxation effect induced by cAMP (100 μm). 6-Bnz-cAMP (100 μm) predominantly decreased the tension force in comparison with 8-pCPT-2'-O-Me-cAMP (100 μm).

CONCLUSIONS

We showed that cAMP predominantly inhibited the ROK pathway but not the PKC pathway. The PKA-dependent pathway is dominant, while Epac plays a minor role in human detrusor smooth muscle Ca(2+) sensitization.

Pioneering drugs for overactive bladder and detrusor overactivity: Ongoing research and future directions

The ongoing research on pioneering drug candidates for the overactive bladder (OAB) aimed to overcome the limitations of currently licensed pharmacotherapies, such as antimuscarinics, β3-adrenergic agents, and botulinum neurotoxin, has been reviewed performing a systematic literature review and web search. The review covers the exploratory agents alternative to available medications for OAB and that may ultimately prove to be therapeutically useful in the future management of OAB patients based on preclinical and early clinical data. It emerges that many alternative pharmacological strategies have been discovered or are under investigation in disease-oriented studies. Several potential therapeutics are known for years but still find obstacles to pass the clinical stages of development, while other completely novel compounds, targeting new pharmacological targets, have been recently discovered and show potential to translate into clinical therapeutic agents for idiopathic and neurogenic OAB syndrome. The global scenario of investigational drugs for OAB gives promise for the development of innovative therapeutics that may ultimately prove effective as first, combined or second-line treatments within a realistic timescale of ten years.

BK channel-mediated relaxation of urinary bladder smooth muscle: a novel paradigm for phosphodiesterase type 4 regulation of bladder function

Elevation of intracellular cAMP and activation of protein kinase A (PKA) lead to activation of large conductance voltage- and Ca(2+)-activated K(+) (BK) channels, thus attenuation of detrusor smooth muscle (DSM) contractility. In this study, we investigated the mechanism by which pharmacological inhibition of cAMP-specific phosphodiesterase 4 (PDE4) with rolipram or Ro-20-1724 (C(15)H(22)N(2)O(3)) suppresses guinea pig DSM excitability and contractility. We used high-speed line-scanning confocal microscopy, ratiometric fluorescence Ca(2+) imaging, and perforated whole-cell patch-clamp techniques on freshly isolated DSM cells, along with isometric tension recordings of DSM isolated strips. Rolipram caused an increase in the frequency of Ca(2+) sparks and the spontaneous transient BK currents (TBKCs), hyperpolarized the cell membrane potential (MP), and decreased the intracellular Ca(2+) levels. Blocking BK channels with paxilline reversed the hyperpolarizing effect of rolipram and depolarized the MP back to the control levels. In the presence of H-89 [N-[2-[[3-(4-bromophenyl)-2-propenyl]amino]ethyl]-5-isoquinolinesulfonamide dihydrochloride], a PKA inhibitor, rolipram did not cause MP hyperpolarization. Rolipram or Ro-20-1724 reduced DSM spontaneous and carbachol-induced phasic contraction amplitude, muscle force, duration, and frequency, and electrical field stimulation-induced contraction amplitude, muscle force, and tone. Paxilline recovered DSM contractility, which was suppressed by pretreatment with PDE4 inhibitors. Rolipram had reduced inhibitory effects on DSM contractility in DSM strips pretreated with paxilline. This study revealed a novel cellular mechanism whereby pharmacological inhibition of PDE4 leads to suppression of guinea pig DSM contractility by increasing the frequency of Ca(2+) sparks and the functionally coupled TBKCs, consequently hyperpolarizing DSM cell MP. Collectively, this decreases the global intracellular Ca(2+) levels and DSM contractility in a BK channel-dependent manner.

Phosphodiesterase types 3 and 4 regulate the phasic contraction of neonatal rat bladder smooth myocytes via distinct mechanisms

Activation of the cyclic AMP (cAMP) pathway reduces bladder contractility. However, the role of phosphodiesterase (PDE) families in regulating this function is poorly understood. Here, we compared the contractile function of the cAMP hydrolyzing PDEs in neonatal rat bladder smooth myocytes. RT-PCR and Western blotting analysis revealed that several isoforms of PDE1-4 were expressed in neonatal rat bladder. While 8-methoxymethyl-3-isobutyl-1-methylxanthine (a PDE1 inhibitor) and BAY-60-7550 (a PDE2 inhibitor) had no effect on the carbachol-enhanced phasic contractions of bladder strips, cilostamide (Cil, a PDE3 inhibitor) and Ro-20-1724 (Ro, a PDE4 inhibitor) significantly reduced these contractions. This inhibitory effect of Ro was blunted by the PKA inhibitor H-89, while the inhibitory effect of Cil was strongly attenuated by the PKG inhibitor KT 5823. Application of Ro in single bladder smooth myocytes resulted in an increase in Ca(2+) spark frequency but a decrease both in Ca(2+) transients and in sarcoplasmic reticulum (SR) Ca(2+) content. In contrast, Cil had no effect on these events. Furthermore, Ro-induced inhibition of the phasic contractions was significantly blocked by ryanodine and iberiotoxin. Taken together, PDE3 and PDE4 are the main PDE isoforms in maintaining the phasic contractions of bladder smooth myocytes, with PDE4 being functionally more active than PDE3. However, their roles are mediated through different mechanisms.

Modulation of non-voiding activity by the muscarinergic antagonist tolterodine and the β(3)-adrenoceptor agonist mirabegron in conscious rats with partial outflow obstruction

Experimental urethral obstruction in rats alters micturition patterns with non-voiding activity (NVA) during filling cystometry, showing similarity to that observed in human detrusor overactivity. Several drug classes with therapeutic potential in overactive bladder in humans have been tested in this model in rats, rabbits or guinea pigs, but no detailed analysis of drug effects on cystometric patterns has been published. The present study uses a rat model of overactivity with partial bladder outflow obstruction (BOO) in combination with the procedures to analyse NVA to study the effects of the anticholinergic drug tolterodine and the novel β(3)-adrenoceptor agonist mirabegron. The current data for the first time show that NVA in rats with BOO is sensitive to both the muscarinergic antagonist tolterodine and the β(3)-adrenoceptor agonist mirabegron, but with clear differences between the two drugs: during progression of bladder filling, tolterodine affected both the amplitude and frequency of NVA whereas mirabegron affected primarily the frequency. In addition, tolterodine dose-dependently reduced voiding contractions, while mirabegron did not. A model is proposed to account for these observations where both agents act on a 'pacemaker-like' mechanism which is sensitive to cholinergic excitatory and beta-adrenergic inhibitory inputs. Such concepts could provide insights into the nature of overactive bladder and the site of action of key therapeutic drugs.

OBJECTIVE

To investigate the hypothesis that tolterodine and the β(3)-adrenoceptor agonist mirabegron exert their actions on the motor component of the motor/sensory system in the bladder wall: non-voiding activity (NVA).

MATERIALS AND METHODS

The present study used standard cystometric techniques and a conscious rat model of partial bladder outflow obstruction (BOO). A single dose of either tolterodine (0.01, 0.1 0.3 or 1.0 mg/kg) or mirabegron (0.03, 0.1, 0.3, 1.0 or 3.0 mg/kg) was given i.v. to each animal.

RESULTS

In the dose ranges used, tolterodine reduced the voiding contraction amplitude, whereas mirabegron did not. Non-voiding activity consisted of small (<0.6 mmHg) and large (>0.6 mmHg) transients. As a fill progressed, both tolterodine and mirabegron reduced the cumulative activity of the large non-voiding contractions, but had little effect on the small transients. Tolterodine affected both the amplitude and frequency of NVA, whereas mirabegron affected primarily the frequency.

CONCLUSIONS

Non-voiding activity is sensitive to muscarinergic antagonists and β(3)-adrenoceptor agonists, but there are clear differences between the two drugs. A model is proposed to account for these observations where both agents act on a 'pacemaker-like' mechanism with cholinergic excitatory and adrenergic inhibitory inputs. Such concepts may provide insights into the nature of overactive bladder and the site of action of key therapeutic drugs.

Constitutively active phosphodiesterase activity regulates urinary bladder smooth muscle function: critical role of KCa1.1 channel

Pharmacological blockade of cyclic nucleotide phosphodiesterase (PDE) can relax human urinary bladder smooth muscle (UBSM); however, the underlying cellular mechanism is unknown. In this study, we investigated the effects of PDE pharmacological blockade on human UBSM excitability, spontaneous and nerve-evoked contractility, and determined the underlying cellular mechanism mediating these effects. Patch-clamp electrophysiological experiments showed that 3-isobutyl-1-methylxanthine (10 μM), a nonselective PDE inhibitor, caused ∼3.6-fold increase in the transient K(Ca)1.1 channel current frequency and ∼2.5-fold increase in the spontaneous transient hyperpolarization frequency in UBSM-isolated cells. PDE blockade also caused ∼5.6-mV hyperpolarization of the UBSM cell membrane potential. Blocking the K(Ca)1.1 channels with paxilline abolished the spontaneous transient hyperpolarization and the hyperpolarization effect of PDE blockade on the UBSM cell membrane potential. Live cell Ca(2+)-imaging experiments showed that PDE blockade significantly decreased the global intracellular Ca(2+) levels. Attenuation of PDE activity significantly reduced spontaneous phasic contraction amplitude, muscle force integral, duration, frequency, and muscle tone of human UBSM isolated strips. Blockade of PDE also significantly reduced the contraction amplitude, muscle force integral, and duration of the nerve-evoked contractions induced by 20-Hz electrical field stimulation. Pharmacological inhibition of K(Ca)1.1 channels abolished the relaxation effects of PDE blockade on both spontaneous and nerve-evoked contractions in human UBSM-isolated strips. Our data provide strong evidence that in human UBSM PDE is constitutively active, thus maintaining spontaneous UBSM contractility. PDE blockade causes relaxation of human UBSM by increasing transient K(Ca)1.1 channel current activity, hyperpolarizing cell membrane potential, and decreasing the global intracellular Ca(2+).

Evaluating the significance of cyclic adenosine monophosphate-mediated signaling in human prostate: a functional and biochemical study

OBJECTIVE

To investigate further the potential significance of the cyclic adenosine monophosphate (cAMP) pathway in the control of prostate smooth muscle. The cAMP pathway has been assumed to be an alternative pharmacologic target to treat dysfunctions of the human lower urinary tract. To date, only a few studies have addressed the physiologic relevance of cAMP signal transduction in the control of human prostate function.

METHODS

Phosphodiesterase activity was isolated from microsomal fractions prepared from prostatic tissue and subjected to biochemical analysis. Using the organ bath technique, the effects of the phosphodiesterase type (PDE)4 inhibitors Ro 20-1724, rolipram, and RP 73401 on the tension induced by norepinephrine of isolated prostatic tissue were investigated and compared with the PDE5 inhibitor sildenafil and BAY 13-1197, a nitric oxide-independent activator of the soluble guanylyl cyclase. Statistical analysis was conducted using the Gosset t test.

RESULTS

Biochemical analysis of the microsomal fraction revealed only a single peak of PDE activity that was sensitive to papaverine and the PDE4 inhibitors rolipram and Ro 20-1724. The tension induced by norepinephrine was reversed by the drugs with the following order of efficacy: Ro 20-1724, RP 73401, rolipram, sildenafil, and BAY 13-1197. Pre-exposure of the tissue to a threshold concentration (0.05 μM) of forskolin (adenlyl cyclase activator) increased the reversion of tension induced by rolipram and RP 73401 and the PDE5 inhibitor sildenafil.

CONCLUSION

These results have provided evidence for the significance of cAMP signaling in the control of prostate smooth muscle.

Functional bladder problems in children: pathophysiology, diagnosis, and treatment

Functional lower urinary tract problems, bladder and bowel problems, or dysfunctional elimination syndrome are all terms that describe the common array of symptoms that include overactive bladder syndrome, voiding postponement, stress incontinence, giggle incontinence, and dysfunctional voiding in children. This article discusses the nomenclature and looks at the pathophysiology of functional bladder disorders from a different perspective than has been the norm in the past. Some standard medical treatments as well as some newer forms of treatment are outlined. Treatment algorithms for urinary frequency and urinary incontinence have been created to help the practitioner manage the patient.

Sildenafil effect on the human bladder involves the L-cysteine/hydrogen sulfide pathway: a novel mechanism of action of phosphodiesterase type 5 inhibitors

BACKGROUND

Phosphodiesterase type 5 inhibitors (PDE5-Is) are effective in the treatment of lower urinary tract symptom (LUTS), although their mechanism of action is still unclear. PDE5-Is cause bladder detrusor relaxation, and this effect is partially independent of nitric oxide. Hydrogen sulfide (H(2)S) is a newly discovered transmitter with myorelaxant properties. It is predominantly formed from L-cysteine by cystathionine-β-synthase (CBS) and cystathionine-γ-lyase (CSE).

OBJECTIVE

To evaluate whether the L-cysteine/H(2)S pathway contributes to the relaxing effect of sildenafil on the human detrusor dome.

DESIGN, SETTING, AND PARTICIPANTS

Samples of bladders obtained from men undergoing open prostatectomy for benign prostatic hyperplasia (BPH) were used. The presence of CBS and CSE enzymes was assessed by western blot. H(2)S production was measured by a colorimetric assay in basal and stimulated conditions with L-cysteine and in response to sildenafil (1, 3, 10, and 30 μM), 8-bromo-cyclic guanosine monophosphate (8-bromo-cGMP; 100 μM) or dibutyryl-cyclic adenosine monophosphate (dibutyryl-cAMP; 100 μM). A curve concentration effect of sodium hydrosulfide (NaHS), H(2)S donor (0.1 μM to 10mM), L-cysteine (0.1 μM to 10mM), and sildenafil (0.1-10 μM) was performed on precontracted detrusor dome strips. To investigate H(2)S signaling in a sildenafil effect, CBS and CSE inhibitors were used.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

Analysis of variance was used, followed by the Bonferroni post hoc test.

RESULTS AND LIMITATIONS

CBS and CSE are present in the human bladder dome and efficiently convert L-cysteine into H(2)S. Both NaHS and L-cysteine relaxed human strips. Sildenafil caused (1) a relaxation of bladder dome strips and (2) a concentration-dependent increase in H(2)S production. Both effects were significantly reduced by CBS and CSE inhibitors. Similar to sildenafil, both 8-bromo-cGMP and dibutyryl-cAMP caused an increase in H(2)S production.

CONCLUSIONS

The sildenafil relaxant effect on the human bladder involves the H(2)S signaling pathway. This effect may account in part for the efficacy of PDE5-Is in LUTS. A better definition of the pathophysiologic role of the H(2)S pathway in the human bladder may open new therapeutic approaches.

Inhibition of phosphodiesterases relaxes detrusor smooth muscle via activation of the large-conductance voltage- and Ca²⁺-activated K⁺ channel

Detrusor smooth muscle (DSM) exhibits increased spontaneous phasic contractions under pathophysiological conditions such as detrusor overactivity (DO). Our previous studies showed that activation of cAMP signaling pathways reduces DSM contractility by increasing the large-conductance voltage- and Ca(2+)-activated K(+) (BK) channel activity. Here, we tested the hypothesis whether inhibition of phosphodiesterases (PDEs) can reduce guinea pig DSM excitability and contractility by increasing BK channel activity. Utilizing isometric tension recordings of DSM isolated strips and the perforated patch-clamp technique on freshly isolated DSM cells, we examined the mechanism of DSM relaxation induced by PDE inhibition. Inhibition of PDEs by 3-isobutyl-1-methylxanthine (IBMX), a nonselective PDE inhibitor, significantly reduced DSM spontaneous and carbachol-induced contraction amplitude, frequency, duration, muscle force integral, and tone in a concentration-dependent manner. IBMX significantly reduced electrical field stimulation-induced contractions of DSM strips. Blocking BK channels with paxilline diminished the inhibitory effects of IBMX on DSM contractility, indicating a role for BK channels in DSM relaxation mediated by PDE inhibition. IBMX increased the transient BK currents (TBKCs) frequency by ∼3-fold without affecting the TBKCs amplitude. IBMX increased the frequency of the spontaneous transient hyperpolarizations by ∼2-fold and hyperpolarized the DSM cell resting membrane potential by ∼6 mV. Blocking the BK channels with paxilline abolished the IBMX hyperpolarizing effects. Under conditions of blocked Ca(2+) sources for BK channel activation, IBMX did not affect the depolarization-induced steady-state whole cell BK currents. Our data reveal that PDE inhibition with IBMX relaxes guinea pig DSM via TBKCs activation and subsequent DSM cell membrane hyperpolarization.

Phosphodiesterase (PDE) inhibitors in the treatment of lower urinary tract dysfunction

Several disorders of the human upper and lower urinary tract, such as urinary stone disease, lower urinary tract symptoms (LUTS) due to benign prostatic hyperplasia (BPH) and detrusor overactivity, can be therapeutically addressed by influencing the function of the smooth musculature of the ureter, prostate or urinary bladder, respectively. In order to ensure a drug effect without significant adverse events, a certain degree of tissue selectivity is mandatory. The treatment of said conditions aims to focus on orally available drugs acting via intracellular signalling pathways. Specifically, the cyclic nucleotide monophosphate cyclic GMP represents an important mediator in the control of the outflow region (bladder, urethra). The use of phosphodiesterase (PDE) inhibitors, such as sildenafil, tadalafil, vardenafil, avanafil or udenafil, known to restrain the degradation of the second messenger cyclic GMP, offers great opportunities in the treatment of lower urinary tract dysfunction. PDE inhibitors are regarded as efficacious, have a rapid onset of action and favourable effect-to-side-effect ratio. The role of PDE5 inhibitors in the treatment of BPH/LUTS and the overactive bladder has already been addressed in randomized, double-blind, placebo-controlled trials, as well as preliminary open-label studies enrolling either several hundreds or only 20 patients. The purpose of this review is to focus on the potential use and clinical significance of PDE inhibitors in the treatment of storage and voiding dysfunctions of the lower urinary tract. The strategy of modulating the activity of PDE isoenzymes might represent a novel approach in patients with lower urinary tract dysfunction (LUTD).

Treatment of erectile dysfunction and lower urinary tract symptoms by phosphodiesterase inhibitors

To date, it is widely accepted that several disorders of the male and female urogenital tract, such as erectile dysfunction, bladder overactivity, urinary stone disease, the benign prostatic syndrome, as well as symptoms of female sexual arousal and orgasmic dysfunctions, can be therapeutically approached by influencing the function of the smooth musculature of the respective organs. To achieve a pronounced drug effect without significant adverse events, a certain degree of tissue selectivity is mandatory. Selective intervention in intracellular pathways regulating smooth muscle tone has become the most promising strategy to modulate tissue and organ function. Since the concept of taking a pill to relieve symptoms of lower urinary tract dysfunction is now widely accepted following the successes of phosphodiesterase 5 (PDE5) inhibitor treatment of erectile dysfunction, the treatment of urological diseases has focused on orally available drugs acting via influencing intracellular signaling pathways, thereby combining a high response rate with the advantage of an on-demand intake. Specifically, the use of isoenzyme-selective PDE inhibitors offers great opportunities in the medical treatment of various genitourinary diseases. These agents are regarded to be safe and to be efficacious, i.e., having a fast onset of drug action and an improved effect-to-side-effect ratio. As experience with this class of compounds and their use in urology is rapidly growing, basic and clinical research in this field will most likely expand the pharmacological armamentarium of innovative treatment options in the next few years. The purpose of this review is to summarize current, as well as potential, upcoming indications for the use of PDE inhibitors in the pharmacotherapy of male erectile dysfunction and lower urinary tract symptoms.

Expression of cAMP-dependent protein kinase isoforms in the human prostate: functional significance and relation to PDE4

OBJECTIVES

To investigate the expression of isoforms of the cyclic AMP (cAMP)-dependent protein kinase (cAK) in the transition zone of the human prostate and the functional significance of the enzyme in the control of prostate smooth muscle.

METHODS

Using Western blot analysis and immunohistochemistry, the expression and distribution in the prostate of cAKIalpha, cAKIbeta, cAKIIalpha, and cAKIIbeta in relation to alpha-actin and the phosphodiesterase PDE4 (types A and B) were investigated. The effects of the cAK inhibitor Rp-8-CPT-cAMPS on the reversion of the adrenergic tension of isolated prostate tissue induced by forskolin, rolipram, sodium nitroprusside (SNP), and tadalafil were examined by means of the organ bath technique.

RESULTS

Immunosignals specific for cAKIalpha, cAKIIalpha, and cAKIIbeta were observed in the smooth musculature and glandular structures of the prostate. Double stainings revealed the colocalization of alpha-actin and PDE4 with the cAK isoforms. The expression of the cAK isoforms was confirmed by Western blot analysis. The relaxation of the tension induced by norepinephrine brought about by forskolin, rolipram, SNP, and tadalafil was significantly attenuated by Rp-8-CPT-cAMPS.

CONCLUSIONS

The colocalization of smooth muscle alpha-actin and PDE4 with cAK, as well as the results from the organ bath experiments, provide further evidence for a pivotal role of the cAMP-dependent signaling in the regulation of prostate smooth muscle contractility. Compounds interacting with the cAMP/cAK pathway might represent a new therapeutic avenue to treat symptoms of benign prostatic hyperplasia and lower urinary tract symptomatology.

Signalling pathways involved in sildenafil-induced relaxation of human bladder dome smooth muscle

BACKGROUND AND PURPOSE

The mechanism(s) of action responsible for the beneficial effects of phosphodiesterase 5 (PDE5) inhibitors including sildenafil on lower urinary tract symptoms suggestive of benign prostate hyperplasia are unclear. In particular, the role of the NO-cGMP signalling pathway in regulating human bladder dome smooth muscle relaxation is questionable. Thus, we assessed the ability of a PDE5 inhibitor, sildenafil, to relax such tissue, and identified the signalling pathways involved in this relaxation.

EXPERIMENTAL APPROACH

Human bladder samples were obtained from 20 patients with no overactive bladder undergoing cystectomy for bladder cancer. Detrusor strips were mounted isometrically in Krebs-HEPES solution. Concentration-response curves for sildenafil (10 nM-30 microM) were generated in the presence of various inhibitors on carbachol-induced pre-contraction.

KEY RESULTS

Sildenafil relaxed carbachol-pre-contracted human detrusor strips, starting at 3 microM. This effect was not modified by NO donors, S-nitroso-N-acetylpenicillamine (10 microM) or sodium nitroprusside (300 nM), but was significantly inhibited by inhibition of guanylate cyclase (with ODQ, 10 microM) or adenylyl cyclase (with MDL-12,330A, 10 microM), by the ATP-sensitive potassium channel inhibitor, glibenclamide (10 microM), or inhibition of the large (with iberiotoxin, 30 nM) or small (with apamin, 100 nM) conductance calcium-activated potassium channels.

CONCLUSIONS AND IMPLICATIONS

Sildenafil-induced relaxation of human detrusor smooth muscle involved cGMP-, cAMP- and K(+) channel-dependent signalling pathways, with a minor contribution from NO. The effect of this sildenafil-induced relaxation on the clinical benefit of PDE5 inhibitors on urinary storage symptoms in men deserves further investigation.

New insights into the pharmacology of the bladder

PURPOSE OF REVIEW

Pharmacotherapy of a number of bladder disorders has traditionally focused on targeting the 'sensory' component or bladder nerves and the smooth muscle. This review aims to provide an insight into recent (experimental and clinical) developments in mechanisms of existing therapies as well as novel targets.

RECENT FINDINGS

Traditionally, sensory signaling in the urinary bladder has been attributed to activation of bladder afferents, but new findings have pointed to the urothelium and interstitial cells as key participants in the transduction of sensory events. Recent advances provide strong support for the development of subtype selective receptor agonists/antagonists, the modulation of signal transduction cascades and new and expanded uses for various neurotoxins.

SUMMARY

The development of therapeutic options for the treatment of a number of bladder disorders is complicated, and most treatments are associated with an increased incidence of side effects or lack of specificity. Recent studies suggest that selective targeting of receptors/ion channels or a disease-specific (i.e. phosphorylated) form of the receptor may represent a viable therapeutic target. Though the mechanisms regulating ion channel expression under pathological conditions are not fully known, an increased understanding of these pathways has important implications for drug development.

Rolipram, a specific type-4 phosphodiesterase inhibitor, inhibits cyclophosphamide-induced haemorrhagic cystitis in rats

OBJECTIVE

To investigate the protective roles of type 4 phosphodiesterase (PDE4) inhibitor in cyclophosphamide (CYP)-induced haemorrhagic cystitis, as the PDE4 inhibitor has anti-inflammatory effects but its characterization is still unknown in urinary tract diseases.

MATERIALS AND METHODS

In female Sprague-Dawley rats, CYP was administered intraperitoneally and bladders were harvested 24 h after CYP injection. In another group, rolipram as a PDE4 inhibitor was administered before CYP treatment. The effects and mechanisms of CYP with/without rolipram pretreatment were evaluated by microscopic features, bladder wet weight, myeloperoxidase (MPO) activity, nitric oxide (NO)-metabolite production and expression levels of inflammation-related genes.

RESULTS

CYP injection resulted in severe cystitis. Pretreatment with rolipram significantly reduced the increase in bladder wet weight and MPO activity, and ameliorated histological inflammatory changes caused by CYP. The levels of inflammation-related transcripts including inducible NO synthase (iNOS), interleukin-1beta and tumour necrosis factor-alpha, induced by CYP, were down-regulated significantly by pretreatment with rolipram. Also, rolipram reduced the NO-metabolite production and iNOS protein expression in the immunohistochemical examination.

CONCLUSION

These results indicate that rolipram can attenuate the development of CYP-induced cystitis in rats by suppressing cytokine production and iNOS induction. Thus, treatment with PDE4 inhibitor has potential clinical implications of the prevention of bladder inflammatory diseases.

Effect of phosphodiesterase type 4 inhibitor rolipram on cyclophosphamide-induced cystitis in rats

Cyclophosphamide induces a severe haemorrhagic cystitis characterized by bladder overactivity. The study was conducted to examine effects of a phosphodiesterase 4 (PDE4) inhibitor rolipram on bladder overactivity in rats with cyclophosphamide treatment. 42 female Wistar rats were used. 30 rats received a single i.p. injection of cyclophosphamide, and after 72 h, bladder function was evaluated by (1) in vitro preparations of whole bladders and (2) cystometry with continuous saline infusion under urethane anesthesia. Cyclophosphamide-treatment dramatically potentiated the basal spontaneous contractions of isolated whole bladders compared to control rats. Atropine, guanethidine or suramin was ineffective on the spontaneous contractions whereas nifedipine completely abolished. Rolipram (5-80 microM) induced a significant concentration-dependent decrease on the amplitude, frequency (contractions/min) and area under the curve of spontaneous contractions. Carbachol elicited phasic contractions superimposed on a tonic contraction. Rolipram caused a relaxation on the tonic contraction whereas it could not affect the phasic contractions induced by carbachol. In anesthetized rats, during continuous infusion cystometry, intercontraction interval was significantly shorter in cyclophosphamide-injected rats than in control rats. Rolipram at 5-40 microM has no significant effect on the intercontraction interval and contraction pressure while it significantly decreased pressure threshold. At 80 microM, it significantly decreased the intercontraction interval and contraction pressure. In conclusion, PDE4 inhibitor rolipram caused a significant decrease on the amplitude, frequency and area under the curve of basal spontaneous contractions in cyclophosphamide-treated rats, at doses that have no effect on the carbachol-induced phasic contractions and cystometric parameters. PDE4 inhibitors may be considered as an attractive strategy for the treatment of cyclophosphamide-induced bladder overactivity.

Emerging pharmacological targets in overactive bladder therapy: experimental and clinical evidences

Antimuscarinics are the mainstay of the medical therapy for overactive bladder, but their side effects and often modest success have prompted studies on novel pharmacological approaches. In this paper, we give a systematic literature review of peer-reviewed papers on the subject. Effective nonantimuscarinic treatments are currently scarce, but many new promising compounds are emerging, which target key molecular pathways involved in micturition control. The most promising potential therapeutic targets include: nervous GABAergic, glycinergic, dopaminergic, and serotonergic systems; b-adrenoceptors and cAMP metabolism; nonadrenergic-noncholinergic mechanisms such as purinergic and neuropeptidergic systems; vanilloid receptors; bladder afferent nerves; nonneuronal bladder signaling systems including urothelium and interstitial cells; prostanoids; Rho-kinase; and different subtypes of potassium and calcium channels. Despite the enormous amount of new biologic insight, very few drugs with mechanism of action other than antimuscarinics have passed as yet the proof-of-concept stage. Further preclinical and clinical studies are urgently needed in this rapidly moving field.

The effects of a type 4 phosphodiesterase inhibitor and the muscarinic cholinergic antagonist tolterodine tartrate on detrusor overactivity in female rats with bladder outlet obstruction

OBJECTIVE

To investigate the effects of the selective phosphodiesterase (PDE) type 4 inhibitor IC485 and the widely used antimuscarinic drug tolterodine tartrate on bladder activity in rats with bladder outlet obstruction (BOO), as inhibition of PDE4 leads to elevation of intracellular cAMP levels and relaxation of smooth muscle.

MATERIALS AND METHODS

BOO was induced in female Sprague-Dawley rats by tying a silk ligature around the urethra. Six weeks after inducing BOO, conscious rats were assessed by cystometry with the urethral ligature intact. The effects of IC485 (5, 10 and 50 mg/kg intravenous, i.v.) were examined and compared with those of tolterodine (0.01, 0.1 and 1 mg/kg i.v.).

RESULTS

IC485 (5-50 mg/kg i.v.) decreased the number and amplitude of non-voiding contractions during the storage phase by 63-88% and 49-83%, respectively; IC485 also increased bladder capacity by 28-37%. There was no change in blood pressure after applying IC485. Tolterodine tartrate (0.1 and 1.0 mg/kg) significantly decreased the number and amplitude of non-voiding contractions by 38-74% and 29-44%, respectively, and increased bladder capacity by 19-51%. Whereas voiding efficiency and maximum voiding pressure were not altered by IC485 at any dose, tolterodine significantly reduced both, by 35-67% and 19-34%, respectively.

CONCLUSION

Both IC485 and tolterodine tartrate reduced detrusor overactivity in rats with BOO. In addition, doses of IC485 that suppressed non-voiding contractions had no effect on voiding function. Therefore, selective PDE4 inhibitors deserve further study as potential agents for treating detrusor overactivity in patients with BOO.